Conventional high-frequency antennas are often cumbersome to manufacture. In particular, conventional beam forming antenna arrays require complicated feed structures and phase-shifters that are impractical to be implemented in a semiconductor-based design due to its cost, power consumption and deficiency in electrical characteristics such as insertion loss and quantization noise levels. In addition, such beam forming arrays become incompatible with digital signal processing techniques as the operating frequency is increased. For example, at the higher data rates enabled by high frequency operation, multipath fading and cross-interference becomes a serious issue. Adaptive beam forming techniques are known to combat these problems. But adaptive beam forming for transmission at 10 GHz or higher frequencies requires massively parallel utilization of A/D and D/A converters.
To address the need in the art for improved beam forming antenna arrays, the present inventor disclosed beam forming antenna arrays compatible with wafer scale integration in copending U.S. application Ser. No. 11/074,027, filed Mar. 7, 2005, now U.S. Pat. No. 7,126,542, and U.S. application Ser. No. 11/049,098, filed Feb. 2, 2005, now U.S. Pat. No. 7,126,541, the contents of both of which are hereby incorporated by reference. These applications utilized and expanded upon the beam forming capabilities disclosed by the present inventor in copending U.S. application Ser. No. 10/423,303, filed Apr. 25, 2003, now U.S. Pat. No. 6,885,344, U.S. application Ser. No. 10/423,160, filed Apr. 25, 2003, now U.S. Pat. No. 6,870,503, U.S. application Ser. Nos. 10/422,907, filed Apr. 25, 2003, 10/423,129, filed Apr. 25, 2003, now U.S. Pat. No. 6,963,307, 10/860,526, filed Jun. 3, 2004, now U.S. Pat. No. 6,982,670, and 10/942,383, filed Sep. 16, 2004, the contents of all of which are hereby incorporated by reference in their entirety.
One embodiment of a beam forming antenna system described in the above-mentioned applications is shown in FIG. 1, which illustrates an integrated RF beam forming and controller unit 130. In this embodiment, the receive and transmit antenna arrays are the same such that each antenna 170 functions to both transmit and receive. A plurality of integrated antenna circuits 125 each includes an RF beam forming interface circuit 160 and receive/transmit antenna 170. RF beam forming interface circuit 160 adjusts the phase and/or the amplitude of the received and transmitted RF signal responsive to control from a controller/phase manager circuit 190. Although illustrated having a one-to-one relationship between beam forming interface circuits 160 and antennas 170, it will be appreciated, however, that an integrated antenna circuit 125 may include a plurality of antennas all driven by RF beam forming interface circuit 160.
A circuit diagram for an exemplary embodiment of RF beam forming interface circuit 160 is shown in FIG. 2. Note that the beam forming performed by beam forming circuits 160 may be performed using either phase shifting, amplitude variation, or a combination of both phase shifting and amplitude variation. Accordingly, RF beam forming interface circuit 160 is shown including both a variable phase shifter 200 and a variable attenuator 205. It will be appreciated, however, that the inclusion of either phase shifter 200 or attenuator 205 will depend upon the type of beam forming being performed. To provide a compact design, RF beam forming circuit may include RF switches/multiplexers 210, 215, 220, and 225 so that phase shifter 200 and attenuator 205 may be used in either a receive or transmit configuration. For example, in a receive configuration RF switch 215 routes the received RF signal to a low noise amplifier 221. The resulting amplified signal is then routed by switch 220 to phase shifter 200 and/or attenuator 205. The phase shifting and/or attenuation provided by phase shifter 200 and attenuator 205 are under the control of controller/phase manager circuit 190. The resulting shifted signal routes through RF switch 225 to RF switch 210. RF switch 210 then routes the signal to IF processing circuitry (not illustrated).
In a transmit configuration, the RF signal received from IF processing circuitry (alternatively, a direct down-conversion architecture may be used to provide the RF signal) routes through RF switch 210 to RF switch 220, which in turn routes the RF signal to phase shifter 200 and/or attenuator 205. The resulting shifted signal is then routed through RF switch 225 to a power amplifier 230. The amplified RF signal then routes through RF switch 215 to antenna 170 (FIG. 1). It will be appreciated, however, that different configurations of switches may be implemented to provide this use of a single set of phase-shifter 200 and/or attenuator 205 in both the receive and transmit configuration. In addition, alternate embodiments of RF beam forming interface circuit 160 may be constructed not including switches 210, 220, and 225 such that the receive and transmit paths do not share phase shifter 200 and/or attenuator 205. In such embodiments, RF beam forming interface circuit 160 would include separate phase-shifters and/or attenuators for the receive and transmit paths.
To assist the beam forming capability, a power detector 250 functions as a received signal strength indicator to measure the power in the received RF signal. For example, power detector 250 may comprise a calibrated envelope detector. Power manager 150 (FIG. 1) may detect the peak power determined by the various power detectors 250 within each integrated antenna circuit 125. The integrated antenna circuit 125 having the peak detected power may be denoted as the “master” integrated antenna circuit. Power manager 150 may then determine the relative delays for the envelopes for the RF signals from the remaining integrated antenna circuits 125 with respect to the envelope for the master integrated antenna circuit 125. To transmit in the same direction as this received RF signal, controller/phase manager 190 may determine the phases corresponding to these detected delays and command the transmitted phase shifts/attenuations accordingly. Alternatively, a desired receive or transmit beam forming direction may simply be commanded by controller/phase manager 190 rather than derived from a received signal. In such embodiment, power manager 150 and power detectors 250 need not be included since phasing information will not be derived from a received RF signal.
Regardless of whether integrated antenna circuits 125 perform their beam forming using phase shifting and/or amplitude variation, the shifting and/or variation is performed on the RF signal received either from the IF stage (in a transmit mode) or from its antenna 170 (in a receive mode). By performing the beam forming directly in the RF domain as discussed with respect to FIGS. 1 and 2, substantial savings are introduced over a system that performs its beam forming in the IF or baseband domain. Such IF or baseband systems must include A/D converters for each RF channel being processed. In contrast, the system shown in FIG. 1 may supply a combined RF signal from an adder 140. From an IF standpoint, it is just processing a single RF channel for the system of FIG. 1, thereby requiring just a single A/D. Accordingly, the following discussion will assume that the beam forming is performed in the RF domain. The injection of phase and/or attenuation control signals by controller/phase manager circuit 190 into each integrated antenna circuit 125 may be performed inductively as discussed in U.S. Pat. No. 6,963,307.
Examination of FIG. 1 shows that a network is necessary for the distribution of the RF signals to and from the IF stage to integrated antenna units 125 as well as to and from RF beam forming interface circuits 160 and their corresponding antenna(s) 170. U.S. Pat. No. 7,126,542 discloses a micro-waveguide network for distributing these RF signals. Because of the waveguide transmission, very low transmissions losses were thereby introduced into the distributed RF signals. Moreover, the micro-waveguide network was compatible with wafer scale integration of the resulting beam forming array.
Turning now to FIG. 3, a three-layer wafer scale integrated antenna module (WSAM) 300 is shown in cross-section. WSAM 300 includes a semiconductor substrate 301. On a first surface 302 of substrate 301, antennas such as patches 305 for the integrated antenna circuits are formed as discussed, for example, in U.S. Pat. No. 6,870,503. Active circuitry 310 for the corresponding integrated antenna circuits that incorporate these antennas on formed on a second surface 303 of substrate 301. Thus, WSAM 300 includes the “back side” feature disclosed in U.S. application Ser. No. 10/942,383 in that active circuitry 310 and antennas 305 are separated on either side of substrate 301. In this fashion, electrical isolation between the active circuitry and the antenna elements is enhanced. Moreover, the ability to couple signals to and from active circuitry 310 is also enhanced.
Adjacent to second surface 303 is a micro-waveguide distribution network 315. Network 315 carries the RF signals as discussed above. Thus, network 315 distributes the RF signal to and from the IF processing stage (or direct down-conversion stage depending upon the receiver architecture). In addition, network 315 may carry the RF signals to and from the RF beam forming interface circuits to their corresponding antenna(s).
Network 315 comprises waveguides that may be formed using metal layers in a semiconductor process such as CMOS as discussed in, for example, U.S. Pat. No. 6,870,503. However, it will be appreciated the waveguide diameter is then limited by maximum separation achievable between metal layers in such semiconductor processes. Typically, the maximum achievable waveguide diameter would thus be 7 microns or less, thereby limiting use of the waveguide to frequencies above 40 GHz. To accommodate lower frequency operation, micro-machined waveguides may also be utilized.
As discussed in U.S. Ser. No. 10/942,383, a heavily doped deep conductive junction 320 couples active circuitry 310 to vias/rods 330 that in turn couple to antenna elements 305. Formation of junctions 320 is similar to a deep diffusion junction process used for the manufacturing of double diffused CMOS (DMOS) or high voltage devices. It provides a region of low resistive signal path to minimize insertion loss to antenna elements 305.
Upon formation of junctions 320 in substrate 301, active circuitry 310 may be formed using standard semiconductor processes. Active circuitry 310 may then be passivated by applying a low temperature deposited porous SiOx and a thin layer of nitridized oxide (SixOyNz) as a final layer of passivation. Thickness of these sealing layers may range from a fraction of a micron to a few microns. Surface 303 may then be coated with a thermally conductive material and taped to a plastic adhesive holder to flip substrate 301 to expose surface 302. Substrate 301 may then be back ground to reduce its thickness to a few hundreds of micro-meters.
An electric shield 340 may then be sputtered or alternatively coated using conductive paints on surface 301. Shield 340 forms a reflective plane for directivity and also shields antenna elements 305. In addition, parts of shield 340 forms ohmic contacts to junctions 320. For example, metallic lumps may be deposited on junctions 320. These lumps ease penetration of via rods 330 to form ohmic contacts with active circuitry 310.
Network 315 may be formed in a glass, metallic, oxide, or plastic-based insulating layer/substrate 350. Depending upon the desired propagation frequency in network 315, the thickness of substrate 350 may range from a few millimeters to multiple tens of microns, A rectangular or circular cavity is then etched into substrate 350 to form a waveguide cavity 365. The walls of the cavity may then be metallically coated using silver, copper, aluminum, or gold to provide the waveguide boundaries. Each integrated antenna circuit (FIGS. 1-3) will need a feedline/receptor 370 as discussed, for example, in U.S. Pat. No. 7,126,541. Each feedline/receptor 370 may be formed from as a discrete metallic part having a base pin 375 that is inserted into a metallic lump to form ohmic contacts to active circuitry 310 analogous to the insertion of rods/vias 330. A metallic plate 360 may then be used to seal waveguide cavity 365 to complete micro-waveguide network 315. Because network 315 is metallic, it also may function as a heat sink for cooling active circuitry 310.
Although WSAM 300 advantageously suffers relatively very little loss in signal propagation through network 315, the antenna array capacity is impacted by the relative size necessary for each waveguide chamber 365. In general, such chambers need to be approximately ½ wavelength across as known in the waveguide arts. In turn, however, this minimum width requirement limits the number of antennas that may be integrated into a single wafer as each antenna would require (ultimately) its own waveguide.
Accordingly, there is a need in the art for improved wafer scale antenna modules that accommodate increased antenna array density.